Re: [Haskell-cafe] How to catch all exceptions that could be caught?

12 Jan 2012


      On 01/12/12 17:23, Gregory Crosswhite wrote:
...
Indeed, and in fact this situation is a very natural occurrence whenever
you are writing code that takes an arbitrary IO action, executes it, and
then returns either the result or the exception that it threw. The code
that I last used for this took advantage of catchJust and looked roughly
like the following:
execute :: IO a → IO (Either SomeException a)
execute action =
catchJust
(\e → case fromException e of {Just (_ :: AsyncException) → Nothing; _ →
Just e})
(Right <$> action)
(return . Left)
Cheers,
Greg
Ugh, I have no idea why the spacing got eaten;  it was meant to look like:

execute :: IO a -> IO (Either SomeException a)
execute action =
    catchJust
        (\e -> case fromException e of
            Just (_ :: AsyncException) -> Nothing;
            _ -> Just e
        )
        (Right <$> action)
        (return . Left)

Cheers,
Greg